This invention relates to a method of producing semiconductor photodiodes having an indium antimonide epitaxial layer of one type conductivity onto an indium antimonide substrate of another type conductivity, and more particularly to such a method wherein the antimony in the epitaxial layer is partially replaced by another element.
Epitaxial growth is a process of growing solid material from a suitable environment onto a substrate. The growth is epitaxial when the material grown forms an extension of the crystal structure of the substrate. By the addition of gases comprising donor or acceptor type impurities, the epitaxially deposited layer may be of n-type or p-type conductivity as desired.
It is commonly known that diffusion processes are used to produce the p-type region of pn-InSb photovoltaic detectors. Uniformly n-type doped indium antimonide crystals are enclosed together with p-type dopants such as cadmium or zinc in a sealed quartz ampoule. The diffusion will take place at 450.degree.-500.degree. C. After removal of the diffused substrate, the material is further processed into single or multi-element semiconductor photodiodes by utilizing standard planar or mesh technologies.
These methods require costly and complicated etching and optimization processes which greatly aggravate the establishment of reproducible, thin p-layer regions and fail completely when extremely thin, uniform thicknesses are required. Therefore, the resulting photoelectric devices suffer in their performance characteristics. Still another method being utilized is the growth of an epitaxial layer of indium antimonide having the opposite conductance type on an indium antimonide monocrystal. This method suffers greatly from the nonstoichiometric transport properties of both species, the indium and antimony, which will result in an epitaxial layer of very low quality.
It was, therefore, necessary to find a method of producing indium antimonide single and multi-element detectors according to the epitaxial growth method, which does not have the deficiency of the conventional epitaxial methods.
The main demands placed upon the epitaxial process are restoration of the stoichiometry of the epitaxial layer, to assure equivalent and a sufficient partial pressure of all gas species involved and to apply standard device processing technologies to the production of photoelectric indium antimonide diodes. These requirements can be fullfilled by executing the epitaxial process in an apparatus having the capability of producing epitaxial layers of the desired composition.